(1) Field of the Invention
The present invention relates to a method of projecting circuit patterns, more particularly to a method of exposure which is used for printing circuit patterns on a chip of, for example, a magnetic bubble memory device, when a circuit pattern of the chip is composed of a plurality of circuit pattern portions each being partially different from each other.
The present invention can be adapted not only to a usual exposing apparatus using ultraviolet light but also to an exposing apparatus using, for example, X-rays or electron beams which can repeatedly print a plurality of photoresist patterns on a substrate by changing the relative position of the substrate and light source.
The substrate on which the resist patterns are printed according to the present invention can be a substrate of a magnetic bubble memory chip, a substrate of a semiconductor IC chip, or a substrate of thin film magnetic heads. The method according to the present invention is also useful in making an exposing mask which is used for printing mask patterns on these substrates by using a repeater machine.
(2) Description of the Prior Art
At present, photolithographic technology is used to form microelectronic circuits, used in a device such as a magnetic bubble memory device or a semiconductor IC device, on a wafer of crystalline material.
That is, a pattern forming layer of, for example, metal is formed on the surface of the wafer, made of single crystalline silicone in the case of the semiconductor IC chip and made of single crystalline magnetic garnet in the case of the magnetic bubble chip. The pattern forming layer is coated with a photosensitive coating known as photoresist, or resist. A projector type exposing apparatus is then used to project a plurality of mask patterns in a reduced size on the photoresist coating, while moving the wafer at a constant pitch length. One then dissolves and washes away the exposed portions of the photosensitive resist when a positive-acting resist is used or the unexposed portions of the photosensitive resist when a negative-acting resist is used, thereby leaving a photoresist mask on the pattern forming layer. After the photoresist process, a chemical etching process or a dry etching process is used to form microelectronic circuit patterns from the pattern forming layer on the wafer, and the wafer is cut into chips of unit circuits.
In recent years, the memory capacities of semiconductor memory devices and the integration degree of IC devices have increased considerably. The circuit patterns have consequently become very fine and the size of the chips have increased. Unit circuits constituting single devices are therefore formed by a plurality of exposures.
For example, the memory capacities of magnetic bubble memory devices, i.e., the number of magnetic bubbles stored in magnetic bubble chips, have steadily increased and the diameters of each magnetic bubble representing information have been significantly reduced. Each of the conducting patterns made, e.g., of Au or Al-Cu alloy and each of transfer patterns made of permalloy therefore has become very small.
In a magnetic bubble memory device whose memory capacity is 1 Mbits and which uses bubbles each having a diameter of, for example, 2 .mu.m, the minimum size of each of the circuit patterns is approximately 1 .mu.m. Since a conventional contact-type exposing apparatus which uses an exposing mask having the same size as the circuit pattern cannot form such fine circuit patterns accurately, a projection-type exposing apparatus which projects circuit patterns on a reduced scale of, for example, 1/10 has been used.
Said 1 Mbit magnetic bubble memory chip being approximately 10 mm square, even the highest-precision type of projection-type exposuring apparatus available cannot easily project circuit patterns of 1 .mu.m over the entire 10 mm square area with high precision. Therefore, circuit patterns of such a 1 Mbit magnetic bubble memory device are formed by projecting a 500 Kbit circuit pattern two times side by side using the central portion of the projectable area of the exposing apparatus, which has relatively high resolution, rather than the four corner portions, which have relatively low resolution.
The above-mentioned conventional exposing method results in a unit circuit composed of a plurality of half patterns, each of which is partially different from each other but each of which comprises all the different portions of all the half patterns. After a chip of the unit circuit is completed, bonding wires or the like are used to selectively connect the necessary one portion of each half pattern to a signal path, such as input or output terminals. If it is necessary to interconnect conducting pattern portions of half patterns, bonding wires are used to connect the conducting pattern portions to the printed conducting patterns formed on a ceramic base, after mounting the chip of the unit circuit on the ceramic base.
However, the above-mentioned conventional method results in each of the half patterns necessarily including unnecessary pattern portions, i.e., the portions meant for other half patterns. This prevents the effective use of the area of a chip and limits the integration degree of the device. The need in the conventional method for a wire-bonding process to select the necessary one portion of the half patterns and to interconnect conducting pattern portions of the half patterns complicates the manufacturing process of the device, increases the percentage of the faulty products, and lowers the reliability of the manufactured device. The conventional method moreover does not allow interconnection of propagation patterns such as the transfer patterns of magnetic bubble memory devices which are surrounded by guardrails.